A researcher wanted to engage in the best possible research design to obtain reliable information about the possible cause(s) of a disease. Which design would the researcher choose?

Correct Answer: C

Rationale: The most advantageous research design, because it obtains more reliable information and can more easily establish a stronger temporal relationship between presumed causal factors and their effects, is a longitudinal cohort prospective study. A cross-sectional study examines relationships between potential causal factors and disease at a specific time. A descriptive study focuses on the amount and distribution of health and health problems within a population. A prospective study monitors a group of disease-free individuals to determine if and when disease occurs. A retrospective study compares individuals with a particular condition or disease with those who do not have the disease.

Correct Answer: B

Rationale: Surveillance (B) tracks disease patterns to monitor and control spread (e.g., flu surveillance). Diagnosis (A) and treatment (C) are clinical, while risk factor identification (D) is a study goal, not surveillance.

Correct Answer: C

Rationale: Herd immunity (C) is population resistance when a high proportion are immune (e.g., via vaccination, B), protecting others. A is individual, D is passive.

Correct Answer: B

Rationale: Case definition (B) standardizes criteria for consistent disease identification (e.g., COVID-19 symptoms/tests). A, C, and D are unrelated.

Correct Answer: C

Rationale: Cross-sectional studies (C) snapshot prevalence at one time (e.g., surveys). A is retrospective, B is longitudinal, D is experimental.